Process for producing potentially crimped filaments

ABSTRACT

CRIMPED FILAMENTS OF MELTSPUN SYNTHETIC LINEAR POLYMER ARE MADE BY DRAWING THE FILAMENTS, THE ASYMMETRICALLY HEATING THE DRAWN FILAMENTS BY PASSING THEM IN CONTACT WITH A HEATER A SURFACE MAINTAINED AT A TEMPERATURE BETWEEN 170*C. AND 270*C. THAT THE ANGLE OF DEFLECTION IS LESS THAN 45* AND THEN RELAXING THE FILAMENTS.

United States Patent once- 3,651,193 Patented Mar. 21, 1972 3,651,193 FOR PRODUCING POTENTIALLY CRIMPED FILAMENTS George Edward Barlow, Peter Bernard Checkland, and

Robert Alexander Edington, Harrogate, England, assignors to Imperial Chemical Industries Limited, London, England No Drawing. Continuation-in-part of application Ser. No. 507,648, Nov. 15, 1965. This application Apr. 7, 1969, Ser. No. 814,186

Int. Cl. D01d 5/22 U.S. Cl. 264-168 PROCESS 6 Claims ABSTRACT OF THE DISCLOSURE This is a continuation-in-part application of application Ser. No. 507,648, filed Nov. 15, 1965, now abandoned.

This invention relates to potentially crimped filaments and a process for their production.

A process is known for the manufacture of potentially crimped filaments by heating the filaments on one side only continuously along their length while passing over a narrow surface heated to at least 270 C. and above the melting temperature of the filaments.

A We have now found that useful filaments, albeit with a somewhat diminished amount of crimp, can be obtained when the temperature of the narrow surface is maintained at a temperature at or below 270 C. but below the melting point of the filaments.

According to the present invention therefore We provide a modification of the process for the production of potentially crimped filaments meltspun from synthetic linear polymers selected from the group consisting of polyesters and polyamides and copolymers of these containing a major proportion of said polymers, comprising continuously passing a bundle of filaments across a heater having a narrow flat end or curved surface maintained at a temperature of at least 170 C. but below the melting point of the filament so that the angle of deflection over the narrow surface is less than 45 and under a tension sufficient to hold the bundle against the narrow surface in a manner such that the filaments passing over said narrow surface are heated on one side only, whereby speed contact angle and width of the heater are combined so that a temperature gradient is imparted across the cross-section of the filaments and the filaments acquire a shrinkage potential. This may be followed by a heat relaxation step to bring out the crimp. Whilst the bundle of filaments is heated along its length on one side, individual filaments in the bundle shuflie over each other so that heating varies along the length of the filaments. This temperature gradient and non-uniform heating produces a desirable crimp during subsequent heating and relaxing of the filaments and results in a bulked yarn in which the filaments in the yarn along their length show a helical crimp interrupted with short straight portions. The helices of the crimps of any filament can be displaced in relation to the crimp helices of remaining filaments during the latters path through a hot relax zone and when taken up by suitable means, such as nipping feed rolls.

The process is broadly illustrated in the following block diagram:

Asymmetric heating by passing Meltspin filaments filaments across Heat. of synthetic linear lfil heater maintained relaxto polymer between 170(E and develop below filamen crimp melting point The heater with the narrow surface may be rectangular in section with a flat or convex face for contacting the filaments. The radius of curvature in the convex face surface, if used, affects the resulting crimps per inch in the filaments. Diameters of 025-25 mm. are suitable. The narrow surface may be an electrical resistance wire, connected to a thermostat and a transformer. The wire or surface may be slowly advanced for example transversely to the path of the filaments, to prevent wear in that part over which the filaments pass. The filaments may be passed over the narrow heated surface whilst wet, for example with a lubricant spin finish solution, care being taken that the amount of lubricant is not excessive, because large amounts of lubricant have been found to cause frequent breakage of the filaments.

The filaments should be passed at least once over the narrow surface with as little change in direction as possible to avoid filament breakages. We have found, as stated, that a change in direction of 45 should not be exceeded, for continuous running without breakages. The filaments if in a multifilament yarn or tow, should preferably be spread out into a ribbon when passing over the narrow surface in order to obtain heating on one side of each, or as many filaments as possible.

We also provide an apparatus for carrying out our invention comprising a feed means for the filaments such as a driven feed roll, one or more narrow surfaces such as an electrically heated wire or a. pin or a bar, means for heating the narrow surface and means for forwarding the filaments under tension which may be such so as to stretch the filaments not more than 10% while passing over the heated surface i.e., with a small tension gradient. Alternatively the heated surface may be positioned between feed rolls and draw rolls which are used to draw the filaments in a drawing process as used for drawing cold-drawable synthetic linear polymer filaments.

The heated narrow surface is preferably provided with an indirectly heated member. The surface providing membcr may be made of an abrasion resistant heat conducting material such as tungsten, molybdenum, tungsten carbide or ceramic material. Alternatively the member may be formed of softer metal such as iron, brass, aluminum or alloys containing these metals and having an outer layer of the abrasion resistant material which provided the narrow surface. A thermal sensing device may be arranged near to or in contact with the indirectly heated member preferably close to the surface contacted by the moving filaments in order to measure and/or control the temperature attained by the contacting surface e.g. of the metal strip of wire.

The heated narrow surface may be introduced in a drawing process before the draw rolls or preferably after the draw roll. If desired the filaments may be stretched in their passage over the narrow surface.

Draw ratios between 2:1 to 8:1 depending on the natural draw ratio of the filaments may be used in the process; the filaments may be relaxed before or after windup. Alternatively the filaments may be relaxed after cutting into staple fibres.

Speeds of at least metres per minute may be used, but the preferred speeds are those used for drawing the filaments. Speeds of 1,000 metres per minute have given good results. Because of these high speeds our process can conveniently be used in the drawing process, before the filaments are wound up, as already stated.

The filaments may be of cross-sectional shapes other than solid circular, for example trilobal, hollow circular, cruciform, tape or T shaped. Some advantage in specific volume is obtained using the non-circular cross-section shapes. The bundle of filaments may consist of filaments having a range of deniers but in which each filament is preferably of substantially constant denier along its length.

Filaments made from synthetic linear polymers which have been meltspun can be subjected to our process including polyesters, polyamides, and copolymers of these, containing a major proportion of the aforementioned polymers. The treated filaments may be woven or knitted into fabrics before or after a heat relaxation step during which the crimp is brought out. A hot surface, hot fluids, gases or other known means of heating may be used in the heat relaxation step after passage within narrow surface for relaxing the filaments. Preferably tubes through which a gentle current of hot air flows are used for relaxing the filaments, because of their efficient heat exchange at relatively high filament speeds.

The efficiency of bulking of our yarn may be expressed in terms of the specific volume of the yarn. This may conveniently be measured in apparatus using a deep grooved wheel of known dimensions running at constant speed. The yarn under test is then wound into the groove under standard controlled tension conditions. Weighing of the sample enables the specific volume to be calculated. For example polyethylene terephthalate yarns may exhibit a specific volume in the range 1.8 to 2.2 ccs. per gm., whereas flat yarn has a value of 1.0.

The procedure for measuring the specific volume of the yarn may be carried out using a grooved wheel or spool having an external diameter of 9.3 cm., a core-diameter of 2.4 cm. and a spacing of 1.244 mm. between flanges, giving a winding space having a volume of 7.89 cc. The wheel is placed in an apparatus which enabled it to be driven positively at a constant spindle speed of 600 r.p.m. and the apparatus adjusted so that the initial tension on the yarn fed to the wheel is 0.0933 gms. per denier. During the operation the tension increased somewhat, the extent of this being dependent on the denier of the yarn under test. When the groove is full a limit micro-switch stopped the wheel and the yarn filling the groove is then removed and weighed. A simple calculation gives the specific volume of the yarn under test.

The following examples illustrate but do not limit our invention.

EXAMPLE 1 Samples of 360 denier polyethylene terephthalate yarn having 36 filaments of circular solid section were melt spun, treated with a wet lubricating finish and drawn at a draw ratio of 3.65 to 1 between two rolls, using a heated snubbing pin at a temperature of 90 C. to locate the draw zone. The yarns were each taken over the draw roll at a speed of 1250 feet per minute and were given a 30 change of direction by contact with an electrically heated resistance wire, -080" in diameter, before passing over a roll surface which increased the linear speed of the yarn to cause a stretch of 3% in the yarn passing over the hot wire.

The heated resistance wire had a small thermocouple brazed onto it at a point adjacent to the yarn contact. The yarn samples were run over the system described above at various wire temperatures in the range from 170 C. to a temperature several degrees below the melting point (about 267 C) of the filaments, as indicated by the thermocouple attached to the wire. The yarns produced did not display useful crimp but were wound on to bobbins for a relaxation treatment as described hereunder.

The yarn from each bobbin was unwound over a feed roll running at 150 feet per minute, then for heating and relaxing the yarn was passed over a substantially flat hot plate, 20 cm. in length and at a temperature of 195 C.

plate. The relaxed yarn was wound on to bobbins=at"a- I 4 7 21 7A.: 7 before passing to a take -up roll which allowed a relaxation of 1.36 to 1.4:1 in the yarn as it passed over the hot tension of 7 to 9 gms. after leaving the take-up roll. The yarns were found to have crimped filaments in which the substantially helical crimp was of a random nature, varying in frequency and amplitude in a random manner within each filament and substantially out of phase from one filament to another. 7

Specific volume tests rununder standard conditions as described, were applied to the yarn samples which gave results from 1.4 cc. per gm. to 2.0 cc. per gm. being directly proportional to the wire temperature at which each sample was run.

EXAMPLE 2 Samples of -3 60 denier 36 filament polyethylene terephthalate yarn were melt spun and after being lubricated with a wet finish were wound on to bobbins before being drawn at a speed of 1250 feet per minute to a draw ratio of 3.22:1, [first passing over a heated feed roll at ,a tem-.

perature of 93 C. to locate the draw zone substantially on the heated roll, then passing over a curved ribbonforming guide maintained at a temperature of (SO-65 C.

surface of the strip at an angle of 5 to the surface, the-v surface of the strip was raked back 15 from a rectangular profile and the departure angle of the yarn from the strip surfaces was 20 making a total yarn deflection angle of 25. The tungsten strip was indirectly heated'by contact with an electrically heated block containing a thermocouple fitted as close as possible to the front centre point of the strip contact area. The yarn samples were run over the tungsten strip maintained at a range of contant temperatures, as indicated by the thermocouple in the heater block, from C. at temperature several degrees below the melting point of the filaments, each at an interval of about 5 C.

After leaving the draw roll the drawn and strip-treated yarns were overfed into an air tube assembly in which hot air at a temperature of 205 C. was circulating. The yarns were allowed to relax in the hot air tube using an overfeed ratio of 1.4:1, controlled by a take-up roll before being wound on to packages at a tension of 7 to 9 gm;

The wound samples displayed crimp of a similar nature to that described in Example 2 above. Specific volume tests performed on these yarns, using the method hereinbefore described, gave results from 1.3 cc./gm. to 1.7 cc./gm.

according to the strip temperature at which the samples were run, and in direct proportion thereto.

EXAMPLE 3 "Samples of 360 denier 36 filament polyethylene terephthalate yarn were melt spun and treated as described in Example 1 above. The wound yarns were then separately heat relaxed by passing each over a feed roll at l250fft.

per min. through a tube in which air at a temperature of 205 C. was circulating and in which the differential apparent in the yarns was similar in characteristicsto that produced in Example 2 above. Specific volume tests per formed in these yarns using the standard method gave results from 1.4 cc./gm. to 2.07. cc../.gm. 1

What is claimed is:

1. A process for the production of potentially crimped filaments meltspun from synthetic linear polymers selected from the group consisting of polyesters and polyamides and copolymers of these containing a major proportion of said polymers comprising continuously passing a bundle of substantially drawn filaments of constant denier along their length across a heater having a narrow surface maintained at a temperature between 170 C. and below the melting point of said filaments, deflecting the filaments less than 45 over said surface, maintaining the bundle of filaments under a tension sufficient to hold the bundle against the narrow surface over a distance of about 0.3-3 mm. and sufiicient to stretch the filaments 3-l0% during their passage over said narrow surface, adjusting the speed to at leastlOO metres per minute and up to about 1000 metres per minute, adjusting the contact angle and selecting the width of said narrow surface to heat the filaments asymmetrically below the melting temperature and thereby imparting a temperature gradient across the cross section of the individual filaments which make contact with said narrow surface and thereby imparting a differential shrinkage potential to the filaments which have contacted said narrow surface.

2. A process for the production of potentially crimped filaments according to claim 1 followed by a heat relaxation step to bring out the crimp.

3. A process according to claim 1 in which the heated narrow surface is heated by contact with a heater member.

4. A process according to claim 1 in which the heated narrow surface is introduced in a drawing process after the draw roll.

5. A process according to claim 2 in which the filaments are relaxed by feeding into a tube through which a current of hot air flows.

6. A process as in claim 1 wherein said filaments are terephthalate filaments.

References Cited UNITED STATES PATENTS 2,919,534 1/ 1960 Bolinger et al 2872.l3 X 2,931,089 4/ 1960 Evans 2872.l3 X 2,974,391 3/ 1961 Speakman et al. 2872.l3 X 3,025,584 3/1962 Evans 2872.l3 X 3,112,551 12/1963 Schmeider et al. 2872.l3 X 3,128,527 4/1964 Schulz 2872.13 X 3,334,068 12/1965 Edington et a1. 2872.l3 X

JAY H. WOO, Primary Examiner US. Cl. X.R.

2872.l3, 264-290, 342 RE 

